VPN's can be quite a pain, and is considerably more work than raw SSH. Depending on the VPN, the authentication strength is usually also quite a bit lower than that of SSH with RSA keys. There's also additional overhead. I have both VPN and jump hosts to get into our corporate network, and I most certainly prefer the jump host for convenience and performance.

There is also the user-level access restrictions of sshmux which will be much more difficult to replicate with VPN's. At least with pptpd, I believe it would require putting users on individual subnets with firewall rules restricting access to only their permitted hosts. Long story short, it wouldn't be a feasible solution.